I wouldn't hesitate to order the 4.8i if you don't mind the gas. $3k is chump change for what you get in the performance. $9k is a different story (if ordering identical options). BUT, I'd be scared of the jerkiness of the transmission being reported all over the place. Cross your fingers.

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'08 X5 3.0si - Alpine White / Saddle Brown interior
Specs: Sport Pkg, Premium Pkg, Tech Pkg, Comfort Access, Aero Kit, Style 433 staggered 20s on Conti DWS
Mods: Carbon 35 tint, LED angel eyes, GP Thunder 7500k fogs, H&R 20mm/25mm spacers, clear reflectors, gunsmoke-tinted taillights
Coded: Digital speedo, windows/sunroof/tailgate close via keyfob

X5 pics at Flickr